no sound coming out of left speaker

Hi, i have a numark partymix i connect to my laptop and heaphones using virtual DJ and it works fine, now i have just got a pair of numark n wave 580l speakers to connect, i have connected like it says in the manual, but only music playing from right speaker even tho i have the lead connecting the left and right together. Also the sound coming from the right speaker is dull and buzzing PLEASE HELPP
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